It is well known that during handling and/or testing of the integrated circuit devices, electrostatic charges can be applied inadvertently to input/output pins of the device, held temporarily and subsequently discharged through the device, damaging the device. One method for preventing damage to integrated circuit devices from electrostatic discharge events (ESD) is to connect protection devices, such as diodes or "punch-through" devices, between the input/output pins of the integrated circuit device and the power supply circuits of the devices. Such protection devices clamp or limit positive and negative potentials applied to the input and/or output (I/O) pins to the positive and negative supply voltage levels, respectively. However, such arrangements provide protection from high voltage electrostatic discharge only for integrated circuit devices that provide a common power source for all of the circuits on the integrated circuit device.
To minimize the effects of noise in integrated circuit devices, it is common to localize related circuit portions of the integrated circuit device into a plurality of individual power groups, each including a source of operating voltages for circuit portions of the integrated circuit device for that power group. Typically, the individual power groups are not located adjacent one another and the power groups are not electrically interconnected. Therefore, no intentional electrostatic discharge path is provided between the individual I/O pins of different power groups of the circuit device.
If an electrostatic discharge is applied to and held at an input/output pin of an integrated circuit device, such as during insertion into or removal from a test fixture during testing, for example, the static charge must be discharged externally of the integrated circuit device and the discharge current will take the shortest path and being conducted out through an external input/output pin of the integrated circuit device. If the first pin touched by the input/output pin holding the static charge is not in the same power group, usually the static charge will be discharged over a path that includes circuit portions of the integrated circuit device, causing damage to the integrated circuit device.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an electrostatic discharge protection system for integrated circuit devices that include multiple individual power groups.